Most cases of antenatal HN improve or resolve spontaneously with conservative treatment [2,3]. However, some patients do not show improvement without treatment. Currently no consensus exists regarding the optimal schedule and duration of follow-up for patients with SFU grades 1 or 2 HN. It is unclear what neonates require postnatal evaluation, when postnatal evaluation for HN should start, for how long examinations should be carried out, and the duration of the follow-up [13].
The timing for postnatal resolution of HN is quite variable, occurring over the first few years of life. Despite variability in the underlying diagnoses, mild grades of HN generally show early resolution, with most cases of SFU grades 1 or 2 HN resolving within 12–18 months of age [18–20]. In our study, most cases of SFU grade s 1 or 2 HN showed spontaneous improvement or resolution within 4 years. In particular, since SFU grade 1 HN resolves slower than grade 2, the follow-up period is likely to be longer in many cases. However, a small number of cases showed worsening from SFU grades 1 to 2 or from SFU grades 2 to 3, and this worsening was mainly noted within 6 months of age in our study. A previous study reported the need for surgical intervention in a small percentage of cases of mild-grade HN cases [21]. In another previous report, of 225 kidneys with SFU grade 2 HN, 3 showed worsening of HN to a severe grade [159]. Furthermore, a study showed that SFU grade 3 cases that finally required surgery were identified during follow up [22] and it has been concluded that SFU grade 3 should be more closely monitored than SFU grade 2 [17]. We think that SFU grade 1 patients should undergo follow-up ultrasonography during the next 6 months to 1 year when the grade of HN may worse. After that, for stable cases, it is considered safe to stop close monitoring and increase follow-up intervals for once a year. On the other hand, according to our results, SFU grade 2 patients may worsen to high-grade HN at 6 months or less, so we consider necessary to perform serial ultrasonography. However, after that period, it will be possible to increase the follow-up interval, similar to what is done for SFU grade 1.
Operative repair was not required for any case in our study. Since there were no surgeries, we initially believed that the follow-up interval could be increases. However, our study showed that there is a high probability that HN will reappear soon after it disappears. This reappearance of HN is therefore a new important finding to help answer the question of whether it is sufficient to confirm the first disappearance of HN at the end of follow-up. In our study, once HN disappeared for more than 1 year, no case had reappearance of HN. It has been suggested that the follow-up may be terminated if no reappearance is detected for more than 1 year. In our study, there were 7 cases that showed no improvement after they reappeared. In this study, no patient had been submitted to surgery, but at this time it was only possible to describe the some natural history of the cases. New prospective studies are needed to determine the complete natural history of HN cases.
Chertin et al. reported that 50% of cases requiring surgical intervention underwent surgery within the first 2 years, and almost all cases underwent surgery within the first 4 years [23]. These authors recommended evaluation every 3–6 months during the above-mentioned period [23]. Some authors have proposed that further evaluation is unnecessary for SFU grades 1 or 2 [14, 24]. Others have advised serial ultrasonography until decrease in grade or resolution of HN, or until patients are old enough to communicate symptoms of renal colic [25, 26]. Based on the above results, we propose that the follow-up is terminated when there is a confirmation that HN disappeared and did not return for 1 year, or when low grade HN remains stable for more than 4 years (at this time patient will be old enough to communicate symptoms), while the follow-up interval is increased.
Our study had some limitations. This was a retrospective study. Additionally, follow-up indications were not standardized across the participating physicians. The evaluation grade of HN was based on the SFU classification only; anterior-posterior diameter measurement [27] and UTD classification [28] were not performed. Furthermore, n this cohort we may have included not only ureteropelvic junction obstruction but also other complicating malformations, including asymptomatic vesicoureteral reflux because we do not routinely perform voiding cystourethrography or magnetic resonance imaging in asymptomatic HN patients. The SFU grading system has problems with inter- and intra-rater variability [16, 29]. We tried to minimize the problems by adopting a second single reviewer for all ultrasonography findings; however, the reliability problem for grades 2 and 3 remains [16, 30]. Further studies are needed to overcome these limitations and confirm the findings of the present study.